1. Field of the Invention
The present invention is related to a movable barrier and more particularly, to a motor for driving a movable barrier such as a garage door.
2. Background Description
Movable barrier operators and, more particularly, garage door operators are well known and have become very sophisticated to provide users with increased convenience and security. The amount of drive power for such a barrier operator is usually selected based on a trade off between the need for power to start and continue the door""s motion and the noise and vibration generated by the motor, as well as the availability of electrical power. Generally, it is desirable to have a higher power to open the door due to ice and snow freezing the door down. Also, during safety initiated operations larger amounts of power may be desired to reverse or stop the barrier. A problem is that a higher power motor usually create larger levels of noise and vibration and require more electrical power and thus, generate more heat to operate for the same level of mechanical power.
For example, in a situation where the door has become extremely heavy such as when the door""s counter balance spring has broken and the door is required to reverse, a low power motor which is adequate to keep a door in motion may not have enough power to overcome both the inertia of motion and the extreme weight of the door. Typically, in selecting a drive motor for a barrier operator, safety takes precedence over noise and vibration or operational electrical efficiency and, the motor is selected to open the garage door in all situations.
By contrast selecting a high power motor allows the operator to have enough power to lift the door even when the door""s spring has broken. In this situation the high power operator has the ability to open the door but is often more inefficient and has higher levels of, noise and vibration.
The typical motor used in such a garage door operators is a single phase motor. A single-phase motor may be classified as a split phase motor, a permanent split capacitor (PSC) motor, a capacitor start-induction run motor or a capacitor start-capacitor run motor. Further, most single-phase induction motors require a switching arrangement for starting the motor, e.g., switching start windings, a start capacitor, a run capacitor or a combination thereof, to assist the motor in reaching full speed. Capacitor start motors have a start capacitor that is only used to start the motor.
Thus, there is a need for a motor than can have higher power during intervals that require it, yet switch to a lower power, to reduce electrical power requirement and noise and vibration.
The present invention is an asymmetric drive motor and apparatus with the asymmetric drive motor for opening and closing a moveable barrier. The asymmetric drive motor may drive for example, a garage door open at a first drive power and closed at a second drive power. The first drive power is greater than the second drive power. A motor control circuit receives control commands and controls the motor to provide the first drive power if barrier is being opened and at the second drive power if the barrier is being closed.
Accordingly, the asymmetric motor of the present invention has improved power control for selecting higher power or lower power. Further, momentary application of higher power is available if needed at the start of travel for example to overcome inertia or ice that may have frozen the barrier shut. In emergency situations such as when the barrier has encountered an object on closing higher power is available to quickly open the barrier. Further, a power can be adjusted in the motor depending on the load driven by the motor.